[Treatment of acute, first-time posterior shoulder instability]

Posterior shoulder instability is a complex and frequently underdiagnosed condition. In the context of primary manifestation, first-time (sub-)luxation (Moroder type A1) are distinguished from first-time traumatic dislocation (Moroder type A2). Posterior shoulder dislocation is particularly difficult to diagnose in emergency settings and is often overlooked.

Clinical findings include a prominent coracoid and loss of active and passive external rotation. Radiographic features such as the lightbulb sign, vacant glenoid sign, or rim sign may be present, yet the diagnosis is still missed in up to 50% of cases. In cases of uncertainty, CT is recommended to confirm the diagnosis, identify concomitant proximal humeral fractures, and evaluate relevant posterior glenoid bone loss (pGBL) and the presence of a reverse Hill-Sachs lesion (RHSL).

In the acute setting, acute dislocations without associated fracture undergo closed reduction under procedural sedation. In cases of locked dislocation, fracture-dislocation or irreduciblity, early open reduction with definitive management is required. The definitive therapeutic strategy depends on the patient's age, the duration of the dislocation, their functional demands, and the presence of concomitant lesions. Subluxations (A1) can usually be managed conservatively or with arthroscopic posterior labral repair, whereas traumatic first-time dislocations (A2) require careful assessment of the RHSL, posterior labrum, pGBL and rotator cuff. Treatment options, depending on the gamma angle of the RHSL as described by Moroder, include arthroscopic disimpaction, the modified McLaughlin procedure, or open segmental reconstruction.